The present invention relates in general to aerators, and, more particularly, to aerators for use in ponds, and the like.
Growth in the catfish industry from less than 100 acres of ponds in 1955 to over 40,000 acres in 1970 is indicative of the industry's potential. The production of one ton per acre per year through extensive culture versus the production of two-and-a-half tons per acre in intensive culture indicates the effect aeration and circulation can have on fish in a large pond system. Furthermore, the small experimental pond production rate of 10 tons per acre in a 210-day experiment indicates that intensive management of a closed loop water system has possibilities for further refinement.
In addition to higher production, intensive catfish culture has other attractive aspects. Feeding and harvesting operations can be simplified and more easily mechanized. The fish are more readily observable for disease control and growth rate. Predators and other unwanted large pond inhabitants are more easily eliminated. However, some aspects of intensive culture can be detrimental to profitable production. The problems of waste disposal and continuous good water quality are foremost, including the costs which aeration and circulation originate.
A low level of dissolved oxygen in catfish ponds has long been recognized as a major cause of fish kills.
On a sunny day, the plant life in a catfish pond manufactures oxygen rapidly enough to boost the pond water oxygen concentration up to supersaturated levels. It is not uncommon to measure 10-14 parts per million (p.p.m.) of oxygen even though the saturation level is only 7 or 8 p.p.m. At least this is true in the top few feet of pond water penetrated by sunlight. Beneath the level of light penetration, if there is no top to bottom water movement, the oxygen concentration may be near zero p.p.m. Catfish cannot survive in water in which oxygen concentration has dropped below about 1.0 p.p.m.
Since oxygen depletion is the most common cause of massive fish kills, it is beneficial to maintain adequate levels of dissolved oxygen in the deeper locations of the pond. This allows for a more continuous oxidation of waste products and increases the total reserve of oxygen available in the pond.
Combination of warm weather and cloudy days in late summer can result in low oxygen levels for fed catfish ponds. The critical period is likely to be just after sunrise when overnight demands have depleted the oxygen storage in the water, and resupply by photosynthesis has not been activated. When oxygen levels drop below about 3 p.p.m., catfish will usually not feed with enthusiasm. As above-mentioned, oxygen levels below 1.0 p.p.m. are likely to lead to massive fish kills.
Oxygen deficiency is a result of increased oxygen demands of fish populations, surrounding biota, and the oxidation of feed residues produced through intensive fish culture. Stratification of pond water, creating an oxygen-poor lower level, the decrease in oxygen solubility with increasing water temperature, and the decrease in photosynthetic oxygen production caused by a series of cloudy days will increase the danger of oxygen deficits.
Several types of mechanical aerators have been used to maintain an adequate dissolved oxygen level in catfish ponds. These aerators include air blowers, submerged pumps, and propellers. Other aerators are disclosed in U.S. Pat. Nos. 3,561,738, 3,595,538, 3,747,904, 3,846,517 and 3,928,512. However, an examination of oxygen transfer theory has shown that use of mechanical aerators may decrease instead of increase pond water oxygen levels. Photosynthetic production of oxygen can result in supersaturated concentrated levels while the maximum level attainable using mechanical aeration is saturation.
Therefore, there is need for a device which aerates without splashing, bubbling or spraying.